Tire-related additives distribution in roadside soils and uptake by native plants: Insights from laboratory and field studies

The toxicity of Tire and Road Wear Particles (TRWP) is mainly linked to organic additives and their transformation products. This study used a dual approach: controlled lab experiments on root uptake in clover, and paired soil-plant sampling from roadside environments, to assess contamination patterns and exposure routes. In soils spiked with 1% tire wear particles, clover roots absorbed tire-related additives and translocated them to leaves, with total concentrations of 15 additives reaching 621 ± 209 ng/g d.w. Roadside soils and plants were also significantly impacted, with concentrations declining exponentially with distance from the road-ranging from 72 to 0.7 ng/g d.w in soils and 777-73 ng/g d.w in plants between 1 m and 10 m. Notably, in pot experiments soil concentrations exceeded plant concentrations, whereas at roadside sites, plants showed much higher concentrations than soil. This contrast suggests that atmospheric deposition, rather than root uptake, is the dominant pathway by which tire-derived additives contaminate plants in real-world conditions. These findings offer key insights into the widespread occurrence of tire-derived compounds in terrestrial environments near roads, and underscore the need for further research to accurately assess the environmental and human health risks posed by this contamination.